1. Field of the Invention
This invention relates to an automobile generator apparatus driven by an automobile engine, for producing electric power equivalent to ordinary household ac line power.
2. Prior Art Statement
There have been proposed various automobile generator apparatuses for producing the equivalent of household ac line power (referred to hereinafter as "ac line power") by using an automobile engine as a power source. One example of such an apparatus is the internal combustion engine-driven generator apparatus disclosed in Japanese Utility Model Public Disclosure No. SHO 59-132398. As shown in the block diagram of FIG. 60, in this prior art system the output from an ac generator 150 driven by an internal combustion engine is supplied to a rectifier circuit 151 which converts it into dc current and the dc output from the rectifier circuit 151 is converted to ac line power by an invertor circuit 152. The invertor circuit 152 is controlled by the output from an oscillator 154 which is supplied with a constant voltage from a constant voltage circuit 153.
However, the aforesaid publication describes only the basic construction of the apparatus in terms of well-known means commonly used in generator apparatuses of this type and is totally silent on such specifics as the method used for adjusting the power output in response to the ac load, the method used for stabilizing the ac line power output, and what type of countermeasures are implemented when an excessively high output voltage is produced.
In fact, however, in the generator apparatus set out in the aforesaid publication, or for that matter in any automobile generator of this type, it is essential to ensure the output of a stable, high-quality ac line power at all times regardless of whether the automobile is stopped (when the engine is idling) or running and irrespective of the size of the ac load. This is the first problem requiring attention.
Moreover, for assuring production of an ac line power output adequate for the load when the automobile is stopped, it is not sufficient to merely provide the throttle mechanism with an actuator for increasing the throttle valve opening angle produced by the throttle lever, but in view of the fact that malfunctioning of the actuator when the vehicle is running could well lead to a serious accident, it is further necessary to provide measures to cope with such a case. This is the second issue requiring attention.
Further, where an invertor is used for producing the ac line power, there is the risk of residual energy stored by the capacitance between the emitter and collector of the switching transistor being discharged to the ac load, or, in the case wither the ac load is an inductive load, the risk that electromagnetic energy stored in the load will discharge to produce a high-voltage output. While the conventional way used to alleviate these problems has been to insert a bleeder resistor in parallel with the ac load, this is an inefficient expedient since electric power is constantly consumed by the bleeder resistor. This is the third problem requiring attention.
While generators to be driven by an engine are generally of the self-exiting type which are capable of field adjustment, it is preferable for saving under-hood space and realizing a simpler mechanical arrangement to use a single-shaft, dual-output generator system. In some single-shaft, dual-output generators the low-voltage output is derived from the center tap of star-connected stator coils and the high-voltage output taken from the ends of the coils, with both outputs being controllable by controlling the field produced by a single field coil. In generators of the single-shaft, dual-output type having a single stator coil, the general practice is to monitor the low-voltage output and, when the low voltage decreases, to restore it to its original level by increasing the flow of exciting current through the field coil to thereby boost the low-voltage output. With this control method, however, the high-voltage output, which is output as including the low-voltage output, is affected by the increase in the low-voltage output and is apt to rise considerably above the permissible maximum. This is the fourth problem requiring attention.
Again, where the ac load connected to the invertor is relatively large or complex, it sometimes happens that the invertor will be subject to an instantaneous overload and the invertor switching transistor, which is easily damaged by instantaneous large currents, may be destroyed. While the conventional way of avoiding such overload situations has generally been to provide an overcurrent protection circuit, this leads to the problem that the output of the invertor circuit is stopped not only at the start of operation but every time during the course of operation that the load becomes momentarily large. This is the fifth problem requiring attention.
There has also been a problem regarding the low-voltage output. In a generator, when the amount of current becomes higher than the rated level, the amount of magnetic leakage becomes large. When the amount of current rises over a certain level, the produced voltage drops off automatically. This is called the self-drooping characteristic of the generator and in a generator exclusively for generating a low-voltage dc output, occurs from around 600 to 700 VA. On the low-voltage side it therefore suffices to use circuit components with a rated current capacity of around 60 A. In the case of the aforementioned single-shaft, dual-output generator having only a single stator coil, however, since it is necessary to take a large amount of power from the generator for use as the ac line power, the current capacity is on the order of 3 kVA, and self-drooping arises from above 3 kVA. Thus in this type of generator, if field control is carried out solely with reference to the monitored low-voltage output, the current flow through the low-voltage side circuit will become larger than necessary at the time the load falls to zero on the high-voltage side. This means that the low-voltage side must be constituted as a circuit capable of standing up under large amounts of power. As a result, a high-capacity rectification diode has to be used on the low-voltage side and it becomes necessary to use a large heat sink for heat dissipation and a large cooling fan. It also becomes necessary to use wire with a large cross-sectional area for the stator coil. The overall result is that the size of the generator becomes large. This is the sixth problem requiring attention.
Still another problem exists in connection with the switching regulator that has conventionally been inserted between rectifier circuit and the invertor circuit for the purpose ,of stabilizing the ac line power output from the inverter circuit. Namely, this switching regulator requires a smoothing filter comprising a choke coil and a capacitor as well as a diode for effectively discharging the energy stored in the choke coil to the load. However, from the fact that the ac line power output has to be on the order of several KVA, it is obvious that these components have to be of a large capacity permitting the flow of large currents. This again increases the size of the apparatus, making it unsuitable for use in an automobile. This is the seventh problem requiring attention.
It must also be noted that the field current through the aforesaid field coil is controlled by a regulator unit and that this regulator unit has a control transistor connected in series with the field coil. This control transistor is driven to control the field current upon receiving a signal representing the generator output voltage. However, if some problem should occur with this control transistor resulting in its collector and emitter becoming fused together in an electrically conductive state, current would pass constantly through the field coil with the very dangerous result that an exceedingly high voltage would be produced. This is the eighth problem requiring attention.
Furthermore, it may sometimes be desired to obtain a larger amount of ac line power than can be output by a single automobile generator apparatus. This can be accomplished by combining the outputs of two or more ac power sources only on the condition that the voltage maximum is substantially the same in the voltage waves of all ac power sources and that the outputs of the respective power sources are of the same frequency and phase. It is thus not possible to obtain the desired large amount of ac power simply by connecting in parallel generator systems of tow or more automobiles. This is the ninth problem requiring attention.
Furthermore, in a single-shaft, dual-output generator of the type mentioned above which provides low-and high-voltage outputs with a stator having a center tap, if the first coil and second coil divided by the center tap are simply wound together in the same slot, the fields produced by the two coils will interfere with each other, reducing the generation efficiency and giving rise to the risk that a voltage exceeding the rated level may be produced when there is no load on the high-voltage side. This is the tenth problem requiring attention.
Also, in a single-shaft, dual-output generator having a plurality of field members, the rotor becomes long because the plurality of members are disposed in a line in the axial direction and this in turn makes the axial length of the armature shaft great. As a result, the iron core of the armature becomes large. This increases the size and weight of the generator and makes it unsuitable as an automobile generator, which by nature must be light and compact. Moreover, when the armature coil is wound continuously on an axially long iron core, air is prevented from circulating between the windings of the armature coil so that the armature coil is not adequately cooled. This is the eleventh problem requiring attention.